Coated organic film and process



July 11, 1961 w. s. ZEHRUNG ln 2,992,133

COATED ORGANIC FILM AND PROCESS Filed 000. 29, 1959 INVENTOR W//vF/'fw5.5077- E/,v/va, zz*

'Winfield .Scott Zehruug III, Buialo,

gpers yin the food, ,drug and United States Patent 2,992,133 COATEDORGANIC FILM AND PROCESS N.Y., assignor to E. I. du Pont de Nemours andCompany, Wilmington, Del., a corporation of Delaware' Filed Oct. 29,19-59, Ser. No. 849,469 4M12-Claims. (Cl. 117-76) ture permeability,:high transparency, Y good flexibility, etc.,

which particularly suit them for wide application as wrapgeneralcommodities Viields. Many .of .these films, however, are essentiallynon-heat sealable lbecause ,of (l) their high melting point andcrystallinity, and/or (2) their tendency to degrade at temperaturesrequired to effect strong heat seals,

`One method for improvingheat-sealability is to provide `these iilmswith -coatings `of other .thermoplastic organic polymeric -materialssuch as polyethylene, polypropylene,

etc., which do have satisfactory heat seal characteristics.

.However, suchcoatings, when applied to both sides of a Abase film-usually cause performance problems on conventional automaticpackagingmachinery. The coated films tendto drag. excessively onthe metalsurfaces and/ or actually stick to the heat sealing elements of thepackaging machines. Furthermore, there is a tendency for anelectrostatic charge to Aform on the surface of hydrophobicthermoplastic films such as .the yaforementioned one-side polymer-coated.iihns. Thiselectrostatic ,charge also serves to interfere with theperformance of these films on automatic packaging equipment by notpermitting l.the films to slide easily over the .metal surfaces.

-Itris -thefprimary object `of this invention, therefore, to provideacne-side polymer-.coated iilm capableof producing commerciallyacceptable lheat seals. Itis another object to produce such a film whilealso .reducing the susceptibility of thelm to electrostatic charges. Itis a further object .of this invention -to .provide a one-sidepolymer-coatedorganic base iilm which may be satisfactorily heat sealed.on conventional mechanical packagingequipment `without sticking toYtheheated surfaces vused for sealing. These land other objects will bemore clearly apparent from the description which follows.

The -foregoing .and related objects are realized `by the presentinvention which,.briey stated, .comprises applying to both sides(surfaces) vof a non-heatsealable organic base film a continuous-coating of a dilute aqueous solution-of'ahygroscopic salt selected fromthe group consisting-of calcium chloride, magnesium chlorideandmagnesium sulfate and a titanium organic compound obtained as the.reaction product of 1 to 4 mols of acetylacetone with 1 mol -of Ianyalkyl titanate containing `from 2 to 4 carbon atoms in the alkyl`group, the weight percent of hygroscopic salt-based on the weight ofhygroscopic salt and rsaid titanium organic compound being 25-6770;drying the coated film to remove solvent and 'tot cure (harden) thecoating thereon; and, thereafter, applying `to one side only of saidcoated film a continuous coating of a heat sealable compositionconsisting essentially' of a polymer of an alpha-olefin` FIGURE lisadiagrammatic cross-.section of onewemhodiment of a coated film inaccordance with-the .present invention, zthe'thcknesses, especiallyofthe coating layers, being greatly enlarged. Therein, polyethylenetereph- 2,992,133 Patented July 11, 1961 Ythe present invention.

By non-heat sealable organic base film as used herevin is meant -anyself-supporting organic iilm which, for all practical purposes, may notbe heat sealed by conventional heat sealing apparatus by reason of (l) ahigh degree of crystallinity (particularly in the case of biaxiallystretched lm), (2) a high melting point, (3) a tendency to degrade attemperatures necessary to be used for sealing, or (4) a material changein dimensions at temperatures utilized for `heat sealing. Typical ofsuch films is the commercially important polyethylene terephthalateiilm, and the invention will be further described with specic reference-to such ilm as the'base iilm to be treated in accordance with thisinvention. Additional examples of non-heat sealable organic base lms arefilms of polystyrene, polyvinyl chloride, regenerated cellulose,copolyesters of ethylene terephthalate and ethylene isophthalate, etc.

The polymeric coating compositions employed for top coating one side ofthe film in accordance with the present invention must be readily heatsealable on conventional sealing apparatus, i.e., must soften at a lowertemperature lthan the base `iilm. Particularly outstanding compositionsare the polymers, i.e., homopolymers and copolymers, of alpha-oleiinssuch as polyethylene, polypropylene, polybutylene, etc.

The process involves treating the non-heat sealable organic base film,vprior to coating w'th the heat sealable polymeric composition, with anaqueous solution containing at least one of a vspecific class oftitanium organic compounds and at least one of a group of speciiichygroscopic salts. Treatment may be accomplished by dipping the lilm inthe solution, brushing or painting the iilm with the solution, sprayingthe iilmvwith the solution using a gravure type press, etc. The methodof applying the sol-ution is not critical.

The titanium organic compounds in the solution are those compounds,hereinafter referred to as 'titanium acetyl acetonates, prepared byreacting from 1 to 4 mols of acetyl acetone with one mol of an alkyltitanate containing from 2 to 4 carbon atoms in the alkyl group, eg.,tetraisopropyl titanate. The preparation of these compounds isdescribedin copending U.S, applications Serial Nos. 652,375 and 652,376,filed to Harold C. Brill on April 12, 1957, and assigned to the assigneeof the present application.

They can be prepared by simply mixing together acetylacetone and analkyl titanate in the ratio of l to 4 mols of `acetylacetone per mol ofalkyl titanate. The preferred reacting proportions are 2 mols ofacetylacetonate per mol of alkyl titanate. A reaction occurs asevidenced by the evolution of heat and the production of a by-productalcohol corresponding to the alkyl group in the titanium. The reactionmixture is a liquid containing an alkyl titanate-acetylacetone reactionproduct and an alkyl alcohol corresponding to the alkyl `groups in theester used as the reactant. :The alcohol can be removed by distillation,but it is preferred 'to leave it in the solution. The reaction mixtureforms a .precipitate when added to water in amounts which exceed about3%. However, more concentrated, aqueous solutions of the reactionmixture in which the `latter may form as much as vby Weight of lthesolution without undesirable precipitation may lbe formed by anadjustment of the'pH of the solution to be- Ylow about 4.5 by theaddition of a water-soluble acid, such present invention, theconcentration of the titanium acetyl acetonate is usually maintainedbelow 5%, i.e., 0.5-5% in the aqueous medium. The aqueous medium inwhich the titanium acetyl acetonate is dissolved is not critical so longas the titanium compound is stable in the aqueous medium and the mediumis sufficiently volatile to be evaporated after the solution is applied.-It should be noted that the claimed process can use aqueous treatingsolutions containing a stabilizing acid, added alcohol, excessacetylacetone or by-product alcohol from the reaction between the alkyltitanate and acetylacetone.

The aqueous solution must also contain a hygroscopic salt selected fromthe group comprising calcium chloride, magnesium chloride and magnesiumsulfate. The amount of the hygroscopic salt added to the titanium acetylacetonate solution will be based upon the weight of titanium acetylacetonate present in solution; the ratio of the Weight of thehygroscopic salt to the weight of titanium acetyl acetonate in solutionshould range from 1:3 to 2:1. The preferred ratio by Weight of salt totitanium compound should range from 1:1.5 to 2:1. The preferred salt iscalcium chloride because of its excellent stability in the titaniumacetyl acetonate solution and its great effectiveness in reducing theelecrtrostatic susceptibility ofthe base film. The selection ofhygroscopic salts is based on several factors. IThe hygroscopic saltmust reduce the electrostatic susceptibility of the one-side polymercoated lm. It must do this without affecting ad- Versely the improvedheat-seal strength obtained, it is believed, by the presence of thetitanium compound in the treating solution. And, the hygroscopic saltmust not detract from the stability of the aqueous solution, i.e., noprecipitation of the titanium compound should occur in the presence ofthe hygroscopic salt for at least 36 hours.

After treating the base lrn, the next step involves drying the film,usually at an elevated temperature. This can readily be accomplished bypassing the tilm through a tunnel drier or other conventional heatingapparatus. The time of exposure to the heat may range from a few secondsto several minutes at temperatures in the range of 100 C. up to thesoftening point of the film. lEvaporation can usually be accomplishedwith a contact time of about 30-60 seconds at 105 C. or less time athigher temperatures.

The concentration of titanium acetyle acetonate deposited on each sideof the film should range between 0.005-0.l% by weight, based 'on thetotal weight of the film, with the preferred range being .0l-.05% byweight of titanium organic compound applied to each side of the lilm.

The polymeric coating composition, i.e., polyethylene or the like, isthen applied. Any convenient method may be used. The extrusion coatingequipment described in British Patent 688,637 may be used; a film of thecoating polymer may be melt pressed on the treated base film; etc.

The product of the present invention, the treated oneside coated lms,satisfy the long existing need in the packaging industry for a durablepackaging tlm which is both readily heat sealable and which gives goodperformance on conventional mechanical packaging equipment. These highlyversatile films are readily applicable to a wide variety of packaginguses such as overwraps (tray wraps, carton wraps, bundling), make and llbags and pouches, contour bottom bags, etc. The outstanding feature ofthese films is their ability to be utilized on conventional packagingequipment 'Without the occurrence of such performance problems asexcessive drag or sticking to the heated surfaces used for sealing,thereby providing packaged units of good appearance and satisfactoryseal strength.

The one-side coated films of the present invention also nd great use inmany electrical applications such as tape cables, binders, insulationprotectors, plasticizer barriers, moisture-barrier impregnant dams,primary insulation and helically or longitudinally wrapped wire andcable.

A particularly important electrical use for the films of the presentinvention is in the form of tapes for primary or secondary insulation inwire and cable Wrapping. The iilms of the present invention whenemployed for this purpose enjoy the following two important advantagesover materials presently employed: Y

(l) The polyethylene coating on the polyethylene terephthalate base filmacts as a non-slip coating, i.e., the strips do not readily slip loosefrom each other during winding.

(2) By wrapping the coated tilm of the present invention under certaintemperature conditions, the polyethylene coated side will seal itself tothe uncoated (polyethylene terephthalate) side. A moisture-proofwrapping is obtained thereby.

Pigments may also be added to the polyethylene coating, thus formingtapes or strips of diierent coloration. The pigmented film may also beprinted, e.g., a white printed number on a black pigmented background.This feature finds great use in the electrical industry foridentification purposes.

The following examples of several specific preferred embodiments willserve to illustrate more clearly the principles and practice of thepresent invention. Example 1 illustrates the best mode `contemplated forcarrying out the invention. iIn the examples, all percentages are byweight unless otherwise stated.

EXAMPLES 1-3 Substantially amorphous polyethylene terephthalate,prepared in accordance with the general procedure described in U.S.Patent 2,465,319 issued to Whinield and Dickson was extruded in the formof thin iilms and oriented by stretching the lm to substantially thesame extent (at least 2.5)( in both the longitudinal direction (LD) andtransverse direction (TD) and heat set at 200-220 C.).

The oriented heat-set films were then treated on both sides with asolution of titanium acetyl acetonate and a hygroscopic salt by passingthe films through conventional coating and drying apparatus normallyemployed for a two-side coating of base lms. The films were threadedaround a roll located in a dip tank containing aqueous titanium `acetylacetonate and a hygroscopic salt and then between two doctor rolls. Thedip tank contained a 1.5% titanium acetyl acetonate-.075% acetic acid-1% hygroscopic salt-water solution. The solution had been prepared byadding one mole of tetraisopropyl titan- Iate to two mols ofacetylacetone with rapid agitation until no further heat was developed,after which the reaction mixture was cooled -to room temperature anddissolved in an equal volume of dilute acetic acid, then diluting thesolution to the desired concentration by adding the necessary amount ofwater `and finally by adding the hygroscopic salt.

After being coated, the films were passed through the conventionalcoating tower at a speed of feet/minute. 'I'he lower section of thecoating tower was maintained at C. and the upper section at 125 C.

The thus treated films were then melt-coated on one side with a layer ofpolyethylene. Polyethylene1 was extruded at a temperature of 300 C. ontoone side of the treated polyethylene terephthalate lm. Conventionalextrusion coating equipment (such as described in British Patent688,637, to Du Pont) was employed to provide coating thicknesses ofabout 0.3 mil.

As a control, a polyethylene terephthalate film was treated on bothsides with a solution containing only the titanium compound and thencoated on one side with a layer about 0.3 mil thick `of polyethylene.

All of the ilms were tested for heat seal strength for both the coated(polyethylene) to coated side and coated A1athon 16 manufactured by E.I. du Pont de Nemours 8a o. Y

, Y to uncoated side and electrostatic susceptibility. The results ofthese tests and the particular hygroscopic salt used inthe examples arelisted in Table I.

t and the stainless steel plate. The charge, thus generated on the iilm,discharges onto the stainless steel' plate'with which it is in contactandis measured by the meter. The

Table I Concentra- Heat-Seal Strength Electrostatic tion of Concentra-(grams/1.5 inches) Susceptibility Solution Titanium 4 tiouof StabilityExample N o. Hygroscopic Salt Compound Hygro- (hours to Added per Sidescopic Salt Coated Coated form pre- (parts/ per Side to to CoatedUncoated clpitate) million) (parts/ Coated Uncoated Side Side million)Side Side 1 Calcium chloride 161 814 1203 357 64. 4 11. 7 N one after675 hours. 2 Magnesium chloride-- 130 656 1190 211 47. 8 13. 2 l168. 3---.A Magnesium sulfate 107 541 1245 315 61.4 58.8 48. Control N nm` 108None 1300 680 116v 137 The heat seal strengths and electrostaticsusceptibilities Were determined as follows:

Heat seal strength (grams 1.5 inches) was measured by cutting a piece ofthe ilm to be tested 4" x 10 with the grain running in the longdirection into two pieces 4" x 5". The two pieces were superimposed sothat opposite surfaces were in contact. The two pieces of superimposediilm were then sealed together at each end at right angles to the ygrainwith a precision sealer. A 5/8" wide sealing bar heated to a temperatureat which the iilm sample was to be sealed (at pounds per square inchpressure) contacted the ends for 0.5 second. The sealed sheets were thencut in half at right angles to the grain. From the center of the fourresulting pieces, 11/2" wide strips parallel to the grain were cut. Theywere then tested by opening each set of strips at the free ends, placingthem in a Suter Testing machine and pulling them apart. The heat-sealstrength was the highest force in grams required to pull the stripsapart. The minimum acceptable heat-seal strength for thecoated-to-coated side 20 bility,

value registered on the meter, the electrostatic susceptiisa relativevalue and is. useful for purposes of comparison. It compares theabilities of lms to accumulate electrostatic charge under the iniiuenceof the friction normally encountered in manipulating or working with thefilms.

EXAMPLE 4 The purpose of this example was to determine the optimumconcentration of calcium chloride in the aqueous solution of titaniumacetyl -acetonate for the purpose of the present invention. Aqueoussolutions containing 1.5% titanium acetyl acetonate and from 0.25% to2.5% calcium chloride were prepared as in Example 1. Polyethylenetereph-thalate film prepared as in Example l was treated with thesesolutions and then coated with polyethylene and finally tested asdescribed in Example 1. The results are presented in Table II. A ratioof 1:1 calcium chlorid to titanium compound seems to produce optimumresults.

Table II Electrostatic Susceptibility Heat-Seal Strength Calcium(grams/1.5 inches) Chloride Concen- Ratio, Test tration CaClg/Ti MachineTest (Weight Compound Coated Coated Percent) Hand Test to to CoatedUncoated Coated Uncoated Side Side 0 0 Severe- 116 137 1, 300 680 0. 251:6 do 135 122 1, 250 570 0. 5 1:3 Moderate.- 127 61 l, 165 403 l. 01:1. 5 Slight.. 64 12 1, 203 357 1. 5 1: 1 9 l, 201 290 2.0 1. 3: 1 10 21, 103 290 2. 5 1. 6:1 4 0 903 180 test is 800 grams/1.5 inches. Theminimum acceptable heat-seal strength for the uncoated-to-coated sidetest is 150 `grarns/ 1.5 inches.

Electrostatic susceptibility may be measured qualitatively orquantitatively. The qualitative test or hand test consists of rubbing al x 10 strip of the ilm to be tested across the trouser leg ten timesand recording the attraction of the iilm sample to ones hand or to awall as none, slight, moderate or severe. The quantitative test ormachine test involves supporting a strip of the film, trimmed to 1" X 4,on land in electrical contact with a ilat, slightly roughened stainlesssteel plate, the plate being connected to a meter for measuringelectrical potential but otherwise insulated from its surroundings. Theplate is roughened by rubbing it lightly with a 120 Carborundurn cloth,making various light 70 the iilm for a distance of 3 between theweighted block 75 weight Having fully described the invention, what isclaimed 1. A process for producing a heat-scalable, organic polymericfilm which comprises treating both sides of a polyethylene terephthalatebase lm with a dilute aqueous solution containing the reaction productof 1 to 4 mols of acetylacetone and 1 mol of an alkyl titanatecontaining 2 to 4 carbon atoms in the alkyl group and a hygroscopic saltselected from the group consisting of calcium chloride, magnesiumchloride and magnesium sulfate, the weight percent of the hygroscopicsalt, based on the weight of hygroscopic salt plus the reaction product,being 25-67%; drying the coated Iilm; and, there after, applying to oneside only of said coated iilm a conltinuous coating of polyethylene.

2. A process as in claim 1 wherein the base lm is biaxiaalily oriented,heat-set polyethylene terephthalate iilm.

3. A process vas in claim 1 wherein said dilute aqueous solutioncontains 0.5-5% oct said reaction product by of acetylacetone and saidalkyl titanate.

7 4. Aprocess as in claim 1 whereinsaid alkyl titanate is tetraisopropyltitanate. n

V5. A process as in claim 1 wherein said hygroscopic salt is calciumchloride.

6. A process as in claim 1 wherein said hygroscopic salt is magnesiumchloride.

7. A process as in claim 1 wherein said hygroscopc salt is magnesiumsulfate.

8. A heat-sealable, organic polymeric lm comprising a polyethyleneterephthalate base lm having on both sides a continuous coating of thereaction product obtained by reacting 1 to 4 mols of acetylacetone with1 mol of an alkyl titanate containing from 2 to 4 carbon atoms in thealkyl group and a hygroscopic salt selected from the group consisting ofcalcium chloride, magnesium chloride and magnesium sulfate and having onone side only a continuous top coating of a heat-scalable polymericcomposition consisting essentially of polyethylene.

9. A film Ias in `claim 8 wherein said reaction product is obtained byreacting acetylacetone with tetraisopropyl titanate. Y@

10. A lm as in claim 8 wherein the hygroscopic salt is calcium chloride.

11. A lm as in claim 8 wherein the hygroscopic salt is magnesiumchloride.

12. A lm as in claim 8 wherein the hygroscopic salt -is magnesiumsulfate.

References Cited in the le of this patent UNITED STATES PATENTS 5Schmidt June 1, 1954

1. A PROCESS FOR PRODUCING A HEAT-SEALABLE, ORGANIC POLYMERIC FILM WHICHCOMPRISES TREATING BOTH SIDES OF A POLYETHYLENE TEREPHTHALATE BASE FILMWITH A DILUTE AQUEOUS SOLUTION CONTAINING THE REACTION PRODUCT OF 1 TO 4MOLS OF ACETYLACETONE AND 1 MOL OF AN ALKYL TITANATE CONTAINING 2 TO 4CARBON ATOMS IN THE ALKYL GROUP AND A HYGROSCOPIC SALT SELECTED FROM THEGROUP CONSISTING OF CALCIUM CHLORIDE, MAGNESIUM CHLORIDE AND MAGNESIUM